WebApi下载附件文件

[RoutePrefix("down")]
    public class FilesController : ApiController
    {

        [GET("file/{id}")]
        public HttpResponseMessage GetSomePdf(string id)
        {
            var path = MyApp.PathToSomePdf(id);
            if (path!= null)
                return FileAsAttachment(path, "somepdf.pdf");
            return new HttpResponseMessage(HttpStatusCode.NotFound);
        }
        public static HttpResponseMessage FileAsAttachment(string path, string filename)
        {
            if (File.Exists(path))
            {

                HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
                var stream = new FileStream(path, FileMode.Open);
                result.Content = new StreamContent(stream);
                result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
                result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
                result.Content.Headers.ContentDisposition.FileName = filename;
                return result;
            }
            return new HttpResponseMessage(HttpStatusCode.NotFound);
        }

public class DataController : ApiController
   {
       // Sample content used to demonstrate range requests     
       private static readonly byte[] _content = File.ReadAllBytes(HttpContext.Current.Server.MapPath("~/Content/airports.csv"));
 
       // Content type for our body
       private static readonly MediaTypeHeaderValue _mediaType = MediaTypeHeaderValue.Parse("text/csv");
 
       public HttpResponseMessage Get(bool IsLengthOnly)
       {
           //if only length is requested
           if (IsLengthOnly)
           {
               return Request.CreateResponse(HttpStatusCode.OK, _content.Length);
           }
           else
           {               
               MemoryStream memStream = new MemoryStream(_content);
 
               // Check to see if this is a range request (i.e. contains a Range header field)               
               if (Request.Headers.Range != null)
               {
                   try
                   {
                       HttpResponseMessage partialResponse = Request.CreateResponse(HttpStatusCode.PartialContent);
                       partialResponse.Content = new ByteRangeStreamContent(memStream, Request.Headers.Range, _mediaType);
                       return partialResponse;
                   }
                   catch (InvalidByteRangeException invalidByteRangeException)
                   {
                       return Request.CreateErrorResponse(invalidByteRangeException);
                   }
               }
               else
               {
                   // If it is not a range request we just send the whole thing as normal
                   HttpResponseMessage fullResponse = Request.CreateResponse(HttpStatusCode.OK);
                   fullResponse.Content = new StreamContent(memStream);
                   fullResponse.Content.Headers.ContentType = _mediaType;
                   return fullResponse;
               }
           }
       }
   }